gander (n.)

"a large waterfowl proverbially noted, I know not why, for foolishness" [Johnson], Old English gos "a goose," from Proto-Germanic *gans- "goose" (source also of Old Frisian gos, Old Norse gas, Old High German gans, German Gans "goose"), from PIE *ghans- (source also of Sanskrit hamsah (masc.), hansi (fem.), "goose, swan;" Greek khen; Latin anser; Polish gęś "goose;" Lithuanian žąsis "goose;" Old Irish geiss "swan"), probably imitative of its honking.

Geese are technically distinguished from swans and from ducks by the combination of feathered lores, reticulate tarsi, stout bill high at the base, and simple hind toe. [Century Dictionary]

Spanish ganso "goose" is from a Germanic source. Loss of "n" sound before "s" is normal in English (compare tooth). Plural form geese is an example of i-mutation. Meaning "simpleton, silly or foolish person" is from early 15c. To cook (one's) goose is attested by 1845, of unknown origin; attempts to connect it to Swedish history and Greek fables are unconvincing. Goose-egg "zero" is attested by 1866 in baseball slang, from being large and round. The goose that lays golden eggs (15c.) is from Aesop.

late 12c., probably from Old English stagga "a stag," from Proto-Germanic *stag-, from PIE root *stegh- "to stick, prick, sting." The Old Norse equivalent was used of male foxes, tomcats, and dragons; and the Germanic root word perhaps originally meant "male animal in its prime."

Adjectival meaning "pertaining to or composed of males only" (as in stag party) is American English slang from 1848. Compare bull-dance, slang for one performed by men only (1845); gander (n.) also was used in the same sense. Stag film "pornographic movie" is attested from 1968. Stag beetle, so called for its" horns," is from 1680s.

"lean and haggard," from or as if from hunger, mid-15c. (as a surname from mid-13c.), of uncertain origin; perhaps from a Scandinavian source (compare Old Norse gand "a thin stick," also "a tall thin man") and somehow connected with the root of gander. Connection also has been suggested to Old French jaunet "yellowish" [The Middle English Compendium].