een zwaluw maakt nog geen zomer

• een zwaluw maakt geen zomer

Ultimately a calque of Ancient Greek μία χελιδὼν ἔαρ οὐ ποιεῖ (mía khelidṑn éar ou poieî), possibly via an intermediary; note that the Dutch has zomer whereas the Greek refers to spring, not summer. This deviation from the original is shared with various languages that borrowed this proverb, including English. This etymology is incomplete. You can help Wiktionary by elaborating on the origins of this term.

• IPA^(key): /eːn ˈzʋaːlyu̯ maːkt noːx ɣeːn ˈzoːmər/

een zwaluw maakt nog geen zomer

1. one swallow does not a summer make

• Also often encountered with emphasis on the first word, then typically spelled with accents marked as één instead of een.