[ Etymonline: ] 1510s, from Latin gerundum "to be carried out," gerundive of gerere "to bear, carry" (see gest). In Latin, a verbal noun used for all cases of the infinitive but the nominative; applied in English to verbal nouns in -ing.
[1.] "So called because according to the old grammarians, the gerund prop[erly] expressed the doing or the necessity of doing something" [Century Dictionary]. ...
1 does not convince me, because it describes other verb forms also (eg: the imperative). So how and what do the ‘gerund' and 'gerundive‘ bear, carry? What underlying semantic notions connect gerere to this grammatical term?
Prof. John Lawler commented
It isn't unique; it's intrinsic to the Conduit Metaphor that underlies traditional views of language. And you'll note that this term was developed by the "old" grammarians -- i.e, Romans, talking about Latin grammar. And Latin gerunds are very different from English gerunds. But the name persists, even though its etymology is silly. Etymologies are often silly; they're ex post facto, like fossil analysis, and they're all based on vanishingly little information. Nobody knows who or when or why or how, but it stuck around, and we're stuck with it. – jlawler May 6 '15 at 0:15
In case you're interested in the Latin etymologies of other grammatical terms, here's a list of them, with links to a Latin dictionary, from my old freshman etymology class. – jlawler May 6 '15 at 0:18