Q: People say things like "if you spend time learning to garden you'll be repaid in spades." I'm sure the reference is to cards, but I wonder what the meaning of the expression is.
A: For the sake of getting the discussion ball rolling, here's some information I found regarding the relation between spade, a garden implement, and spade, a card:
SPADE - "A spade on a playing card is not called a spade because of its resemblance to a digging tool. The word 'spade' meaning 'a tool for digging' is only a distant etymological relative of 'spade' meaning 'a suit of playing cards.' The first 'spade,' the implement, is descended directly from the Old English word 'spadu,' which meant 'a digging tool.' The second 'spade' was borrowed into English from the Italian word 'spada,' which meant 'sword.' 'Spada' is derived via Latin 'spatha' from the Greek word 'spathe,' both words meaning 'broad blade.' 'Spathe' goes back to the same Indo-European form 'spadh' - as does the Germanic ancestor 'spadan' of Old English 'spadu,' so the two words spelled 'spade' are indeed distantly related. A broad-bladed sword was used on Italian playing cards as the symbol of a suit, and this suit was called 'spades' in English. However, the symbol for spades on English playing cards was borrowed not from the Italian sword but from the French pike ('pique' in French). The shape of this pike was probably fashioned after the leaf symbol that appeared on early German playing cards." From "Word Mysteries and Histories" by the editors of the American Heritage Dictionary (Houghton Mifflin Co., Boston, 1986).
Spades is the highest suit in contract bridge, and many other card games where suits are ranked. (Clubs, diamonds, hearts, spades.) It is the most powerful suit, and the relation to winning decisively is a logical extension.