Methinks means it seems to me, in old use. Methinks he protests, methinks not, or so methinks.
It survives only as deliberate archaism and is nearly always a joke now. The lady doth protest too much, methinks is from Hamlet and is the phrase that keeps the word alive. Note that methinks is not me plus thinks: the think in it is a different Old English verb meaning to seem, and the me is a dative — so it means it seems to me rather than I think.
1verbmethinksIt seems to me, in old use.
“Methinks you've had enough cake for one day.”
methinks is an archaic expression.
meTHINKS → ME THINKS
It is me and think, in the older order: me thinks, where we now say I think.
hooks ontothink
Old English me thynceth is from thyncan, to seem, a different verb from thencan, to think. The two verbs merged in modern think, leaving methinks stranded.
Old English
mē
Middle English
me thinketh
English, today
methinks
Built from
From Middle English me thinketh from Old English mē þynceþ (from þyncan (“to seem”)); equivalent to me + think (“to seem”). Compare synonymous Flemish me dunkt, German mir/mich dünkt, Old Norse mér þykkir (Icelandic mér þykir). Compare meseems.
Etymology from Wiktionary, CC BY-SA