簡単【かんたん】
simple, easy, uncomplicated, brief, quick, light
単位【たんい】
unit, denomination, credit (in school), in units of (e.g. "in thousands"), in amounts of
単独【たんどく】
sole, single, solo, independence, singleness, singularity
単純【たんじゅん】
simple, plain, uncomplicated, straightforward, simple-minded, naive
単に【たんに】
simply, merely, only, solely
単なる【たんなる】
mere, simple, sheer
単一【たんいつ】
single, simple, sole, individual, unitary
単価【たんか】
unit price, unit cost
単行本【たんこうぼん】
standalone book (i.e. not part of an anthology, series, etc.), (book published as a) single volume, tankōbon, individual volume of a manga series
単語【たんご】
word, vocabulary
単調【たんちょう】
monotony, monotone, dullness, monotone, monotonic