Merriam-Webster's Collegiate® Dictionary, 11th Edition
SLOG
I. verb (slogged; slogging)
Etymology: origin unknown
Date: 1824
transitive verb to hit hard ; beat , to plod (one's way) perseveringly especially against difficulty, intransitive verb to plod heavily ; tramp , to work hard and steadily ; plug , slogger noun
II. noun
Date: 1888
1. hard persistent work , a prolonged arduous task or effort , a hard dogged march or journey