single, simple, singles (tennis...

simple, easy, uncomplicated...

unit, denomination, credit (in school)...

simple, plain, uncomplicated...

single, one, singular (number)

simply, merely, only...

mere, simple, sheer

word, vocabulary

monotony, monotone, dullness...

sole, single, solo...

standalone book (i.e. not part of an anthology, series, etc.)...

alone, by oneself, unaccompanied...

unit price, unit cost

(single-industry) industrial union

firing one shot at a time, single-shot gun, having only one engine...

winning at the races

tabi, traditional split-toe socks

(intra-company) job transfer away from one's family, unaccompanied posting

English word

single track (railway), single line, solid wire...

simple substance (e.g. chemical), something standing alone, separate item...

single colour (color), monochrome

simplicity and complexity, singular and plural, single and double...

simple interest

simplification

simple average, arithmetic average

C battery, C cell

straight to the point, point-blank, frank...

single sound, monosyllable, phone...

one-horned