Compound Words
Latin builds new words by gluing a prefix to a root, and the prefix is almost always a preposition you already know.
Learn one verb (faciō — make, do) and a handful of prefixes and you've unlocked a whole shelf of vocabulary: cōnficiō (finish off), perficiō (complete through), dēficiō (fail down), sufficiō (supply from under), efficiō (bring out).
Notice what happened to the root. Faciō has an a; the compounds have i. That's vowel weakening — when fa- lands in an unstressed inner syllable, the a dulls to i.
Same with iaciō → ēiciō, capiō → accipiō, teneō → contineō. Once you see the prefix and recognize the weakened root, the meaning is half-translated for you.
A&G also catalog determinative compounds (magnanimus — great-souled), objective compounds (agricola — field-tiller), and inseparable prefixes (re-, dis-, sē-, ne-) that never appear as standalone words.
The Reader rarely tests those by name — but the prefix-plus-verb pattern is the engine of half your vocabulary.
A prefix (usually a preposition) glues onto a root; only the root inflects, and an unstressed root vowel weakens.
Assimilation also bends the prefix to match: ad + ferō → afferō, con + legō → colligō, in + pōnō → impōnō.
See It In Action
— B. C. i. 32
Two compounds in one clause: confectis shows the fa→fe weakening before two consonants, and deducit shows the prefix keeping its adverbial 'down/away' sense intact.
— B. G. i. 49
Three compound verbs in two sentences (prō-, per-, re-). Each prefix carries its own preposition-flavor — forward, through-to-completion, and back — and perficere shows the same a→i weakening as cōnficere.
— B. G. i. 14
Dis- is one of the inseparable prefixes — it never appears as a standalone word, but it's everywhere as a prefix meaning 'apart, away.' Discēdere literally = 'go apart,' and we still hear it in English discede / dissent.
Strip the leading preposition or inseparable particle.
cōnficimus → con- + ficimus
Weakened i came from a; weakened e came from a before two consonants. Long ā stays.
-ficimus → faciō (root fac-)
Prefix-meaning + root-meaning, slightly idiomatic.
con- (together/utterly) + facere (do/make) = 'finish off, accomplish'
per- + adj = 'very X'; sub- + adj = 'somewhat X'; in- + adj = 'not X'.
permāgnus = 'very large'; sub-fuscus = 'darkish'; im-pūrus = 'not pure'
Same two letters, two completely different jobs. One negates an adjective; the other governs a noun.
'not, un-' — fused to an adjective
īnsānus
insane, not sound of mind
'into, in' — governs acc. or abl.
in urbem
into the city
Tip: Ask: is in glued to an adjective with no space, or sitting in front of a noun with its own case? Glued = negative. Free-standing = preposition.
You meet cōnficiunt in the wild and don't know it. What's the most efficient way to crack it?
Study Tips
- •Memorize the prefix table below as a SET — ad-, ab-, con-, dē-, dis-, ex-, in-, ob-, per-, prō-, re-, sub-, trāns-. Each one shows up in a hundred verbs; learning them once pays off forever.
- •When you meet an unfamiliar compound verb, peel off the prefix first, weaken the vowel back (i→a, e→a), and ask whether you know the resulting root. Cōnficere → con- + facere → 'do/make together'.
- •Watch for assimilation in spelling: ad + ferō writes as afferō, con + legō as colligō, in + pōnō as impōnō. The prefix is still there; the consonant just bent to match the next sound.