The Collaborative International Dictionary of English v.0.48:
Fawn \Fawn\, v. i. [imp. & p. p. Fawned; p. pr. & vb. n.
Fawning.] [OE. fawnen, fainen, fagnien, to rejoice,
welcome, flatter, AS. f[ae]gnian to rejoice; akin to Icel.
fagna to rejoice, welcome. See Fain.]
To court favor by low cringing, frisking, etc., as a dog; to
flatter meanly; -- often followed by on or upon.
You showed your teeth like apes, and fawned like
Thou with trembling fear,
Or like a fawning parasite, obeyest. --Milton.
Courtiers who fawn on a master while they betray him.