Vocabulary Building (4)

- complement
(verb) supplement, complete

- complement
(noun) supplement, addition

- compliment
(verb) praise, flatter, commend

- complement
(noun) praise, flattery, commendation

- comprehensive
(adj.) complete, thorough, exhaustive

4.2 - compulsory
(adj.) necessary, obligatory, mandatory

- concede
(verb) admit, acknowledge, recognize

- concise
(adj.) brief, short, abbreviated

- concrete
(adj.) tangible, specific, real, perceptible

- congregate
(verb) assemble, gather

4.3 - conspicuous
(adj.) noticeable, obvious, prominent

- contemplate
(verb) think about, ponder, speculate

- controversial
(adj.) disputable, debatable

- convenient
(adj.) accessible, available, handy

- cope with
(verb) deal with, manage, handle

4.4 - copious
(adj.) abundant, ample, plentiful

- cordial
(adj.) congenial, warm, friendly

- courteous
(adj.) polite, refined, gracious

- covert
(adj.) secret, hidden

- cozy
(adj.) comfortable, warm

- cozy
(adj.) friendly, intimate, close

4.5 - crave
(verb) desire, long for, hope for

- crooked
(adj.) curved, twisted, zigzag

- crooked
(adj.) dishonest, corrupt

- crucial
(adj.) critical, decisive, key

- crude
(adj.) rude, impolite, vulgar

- crude
(adj.) unprocessed, raw, unrefined

4.6 - cruel
(adj.) brutal, vicious, ruthless

- cryptic
(adj.) secret, hidden, mysterious

- curb
(verb) restrict, limit, control

- curious
(adj.) inquisitive

- curious
(adj.) odd, strange, unusual

- curt
(adj.) abrupt, blunt, impolite

Correction:
There's a typo on the 1st post of this thread.
It should be:

- compliment
(noun) praise, flattery, commendation