Green’s Dictionary of Slang

gull-finch n.

[SE gull, a simpleton, a dupe + finch]

a simpleton, a fool.

[UK]J. Taylor Laugh and Be Fat 10: For ’tis concluded mongst the wizards all, / To make thee Master of Gul-finches hall.
[UK]J. Taylor ‘World’s Eighth Wonder’ in Works (1869) II 71: [as cit. 1612].