Where does “complacence” come from?

Complacence comes from Latin complacentia, derived from complaceo, a verb formed from the prefix com- meaning "with" and placeo meaning "to please."

complacence (English): Being complacent; a feeling of contentment or...

Definitions

complacence traces back through two separate lines of ancestry.

Step	Language	Word	Meaning
1	Latin	complacentia	nominative neuter plural of complacēns;...
2	Latin	complaceo	I please or take the fancy of
3	Latin	com-	allomorph of con-
4	Latin	con-	Used in compounds to indicate a being or bringing...
5	Latin	cum	with, along with; at; -fold
6	Old Latin	com	Alternative form of cum
7	Proto-Italic	kom	with, along, at
8	Proto-Indo-European	ḱóm	beside, near, by, with
9	Proto-Indo-European	ḱe	Deictic particle, here; Post-positional...
10	Middle English	kyt	—
11	German	kitt	putty certain kinds of cement used for fixing e.g. window panes
12	Old High German	kuti	—
13	Proto-West Germanic	kwidu	gum, resin
14	Proto-Germanic	kweduz	resin
15	Proto-Indo-European	gʷet-	resin, gum; to say, speak
16	Proto-Indo-European	gū-	to bend; curve; arch; vault; to bow, bend, arch,...

Step	Language	Word	Meaning
1	Latin	complaceō	to please or take the fancy of
2	Latin	cōn-	Used in compounds to indicate a being or bringing together of several objects
3	Latin	-dō	to put
4	Proto-Germanic	-dô	—
5	Sicilian	di	Used to indicate possession, after the thing owned and before the owner; of; ’s
6	Latin	dē	of; concerning; about
7	Latin	post	behind; after, since, besides, except; behind,...
8	Latin	poste	ablative singular of postis
9	Proto-Italic	posti	behind, after
10	Proto-Indo-European	pósti	after
11	Proto-Indo-European	pós	afterwards, post; by, at