“An eastern district of Plymouth whose name means “plum-tree village”, from the Old English plume (plum tree) and tun (village)”, so says Adrian Room in his Dictionary of British Place-names. Another, earlier, authority, Eilert Ekwall agreed and reached a similar conclusion for Plymstock.
There were no such fruity thoughts in the work of Plympton scholar J Brooking-Rowe however; he favoured the idea that this was the settlement of a family of Plyms or Plins. Brooking-Rowe also put forward two other suggestions; Dyer’s, “pen”-“lim or lym”-“ton” three words, Celtic, Gaelic and Saxon respectively, which cobbled together give us “the enclosed space at a port head” and Baxter’s “pilim”-“ton”, the first element of which is associated with “rolling”.
Whatever the explanation all are agreed that Plympton gave its name to the river Plym, which in turn led to the more recent Plymouth.