- (nautical) The navigation of waters free from hazards or unfavourable winds.
- (nautical) Obsolete spelling of
- (by extension) simple, straightforward, or easy
- 2012, Chelsea 6-0 Wolves 
- It was not all plain sailing for Chelsea, however. First David Davis saw his strike tipped over before Slawomir Peszko surged clear of Terry and Cahill and rounded Ross Turnbull before shooting into the side netting.
2007, Hendrik Ibsen, An enemy of the people:
- Plain sailing or no, it has got be be done, anyway
- 1918, Edgar Rice Burroughs, The Land That Time Forgot Chapter IV
- In another fifty yards there was a second turn, this time toward the left! but it was more of a gentle curve, and we took it without trouble. After that it was plain sailing, though as far as I could know, there might be most anything ahead of us, and my nerves strained to the snapping-point every instant.
1853, William Harrison Ainsworth, Ainsworth's Magazine:
- Life is not plain-sailing, and writers on Life must not put themselves in antagonism with their subject
1813, unknown, Good words, Volume 14:
- He's a straightforward, plain-sailing fellow.
- 2012, Chelsea 6-0 Wolves