accepted, age-old, ancient, established, old, traditional
quaint, strange
local, native (esp. AmE)
family
marriage, religious, social

follow, observe, practise/practice (esp. AmE), respect
They still follow the custom of pinning money to the bride's dress.

adopt
learn
know
maintain, preserve, revive

die out, disappear
The custom died out in the 19th century.

prevail, survive
These customs still prevail in remote areas.

according to a/the custom, in accordance with (a/the) custom
They poured wine around the trees in accordance with local custom.

through custom
The rules have grown up through custom and are not laid down by law.

custom of

as is/was the custom
People threw coins onto the stage, as was the custom.

Custom is used with these nouns:
builder, fit, home