- dogged (adj.)
- "having the qualities of a dog" (mostly in a negative sense), c. 1300, from dog (n.). Meaning "persistent" is from 1779. Hence doggedly (late 14c.), "cruelly, maliciously;" later "with a dog's persistence" (1773). Related: Doggedness.
- slog (v.)
- 1824, "hit hard," probably a variant of slug (v.3) "to strike." Sense of "walk doggedly" first recorded 1872. Related: Slogged; slogger; slogging.
- soldier (v.)
- "to serve as a soldier," 1640s, from soldier (n.). Related: Soldiered; soldiering. To soldier on "persist doggedly" is attested from 1954.