What is the morphology of the word significant? At first glance, I see the word sign at the beginning and a probable -ant suffix on the end, which leaves <ific> in the middle. Because sign is a word, I hypothesize that the base is the free base <Sign>. The <ific> is not immediately clear to me, although I wonder if this <ific> is the same as in terrific.
To accurately determine the morphemes, I start by looking up the word in Etymonline and Wiktionary. I immediately learn that Modern English significant comes from Latin significāns. The -āns is a present participle ending that developed into the -ant suffix in English. In the word significant, which is an adjective, the -ant is an adjectival suffix denoting “doing, prone to, or tending to.”
Looking closer at Latin significāns, I find that the word is the present participle of the verb significāre. (The -āre is a Latin infinitive ending.) I then see that significāre comes from signum + -i- + –ficāre. The Latin signum gives English the free base <Sign> denoting “identifying mark, token, indication, symbol, proof,” as I hypothesized. The -um is a Latin singular noun English, which becomes the noun suffix -um in English. Both sign and signum are also words in English.
<Sign → sign>
<Sign + um → signum>
Notice that in the word sign, the <g> is zeroed. In the word signum, the <g> spells [g]. However, for both words, the base is <Sign>. As I have written previously, a base represents the consistent underlying form shared across a word family. Despite the different sounds ([g] versus zero phone) that the <g> spells in related words, the base remains <Sign> across the entire word family.
Other relatives within the <Sign> family include assign, consign, design, designation, resign, signature, signage, and signal, among others.
<as + Sign → assign>
<con + Sign → consign>
<de + Sign → design>
<de + Sign + ate + ion → designation>
<re + Sign → resign>
<Sign + ate + ure → signature>
<Sign + age → signage>
<Sign + al → signal>
Also notice that, in addition to the different phones that the <g> in <Sign> can spell, the <s> can also spell [s] and [z]. In the words design and resign, the <s> spells the voiced [z]. In the words designation and signature, the <s> spells the voiceless [s]. But, again, the base remains <Sign> across the entire word family despite the different ways the words surface in speech.
Returning to the rest of the morphology of significant, I have thus far confirmed the <Sign> base and the -ant suffix. Because significāre comes from signum + -i- + –ficāre, I also know that the <i> following <Sign> is the connecting vowel -i-.
The remaining <fic> comes from the Latin –ficāre, which is a combining form of the Latin facere. A combining form is a form derived from another root or word that occurs only in combination with other elements—typically in compound words—and not as an independent word. Combining forms are conceptually like bound bases in contrast to free bases. In fact, combining forms often developed into English bound bases.
In the word significant, the Latin –ficāre became the bound base <Fice>. I know that the base needs the replaceable <e> to prevent doubling because the <c> does not double when affixed with the vowel-initial -ant.
<Sign + i + Fice + ant → significant>
But is the base most elegantly represented as <Fice> with the replaceable <e>? Returning to my original supposition about the <ific> in significant being the same as in terrific, I decided to look up the word terrific. English terrific comes from Latin terrificus, which comes from terrēre + –ficus. Latin terrēre gives English the bound base <Ter(r)> as in deter and terror. The -ficus comes from facere, which developed into the <Fic> in terrific.
<Ter(r) + i + Fic → terrific>
<de + Ter(r) → deter>
<Ter(r) + o(u)r → terror>
Notice that -ficus comes from facere, which is the ultimate source of –ficāre. I therefore know that the <Fic> in terrific and the <Fice> in significant are forms of the same base. I can thus represent the base parenthetically as bound base <Fic(e)> denoting “make, do, create.” The parenthetical <e> surfaces in some words (significant) but not in others (terrific).
Other words in the <Fic(e)> word family include honorific, horrific, scientific, specific, edifice, suffice, and sacrifice.
<Hono(u)r + i + Fic(e) → honorific> (also spelled honourific)
<Hor(r) + i + Fic(e) → horrific>
<Sci + ent + i + Fic(e) → scientific>
<Spece + i + Fic(e) → specific>
<Ede + i + Fic(e) → edifice>
<suf + Fic(e) → suffice>
<Sac(e)r + i + Fic(e) → sacrifice>
When word-final, the <Fic(e)> can surface as <Fic> or <Fice>. (Notice that the replaceable <e> marks the phonology of the <i> in <Fice> as spelling [ɑɪ] when word final.) The replaceable <e> also surfaces to prevent doubling of the <c> when followed by a vowel-initial suffix.
<Sci + ent + i + Fic(e) + al + ly → scientifically>
<Sac(e)r + i + Fic(e) + ed → sacrificed>
<suf + Fic(e) + es → suffices>
The word significant thus consists of the free base <Sign>, connecting vowel -i-, bound base <Fic(e)>, and suffix -ant.
