【Soil】 , 【dirty】 ,  【sully】 ,  【tarnish】 ,  【foul】 ,  【befoul】 ,  【smirch】 ,  【besmirch】 ,  【grime】 ,  【begrime】  can all mean to make or become unclean.

【Soil】  basically implies fundamental defilement or pollution (as of the mind or spirit) <why war soils and disarranges whatever it touches, I cannot say —Kenneth Roberts >  <making that room our Chapter, our one mind where all that this world soiled should be refined —Masefield >  but in much of its use it applies to a making or becoming superficially and literally unclean (as by spotting or staining or smudging).

In this sense the word is very close to the corresponding sense of  【dirty】 , which is slightly stronger in its implication of uncleanliness and especially of disagreeable uncleanliness; thus, "to  【soil】  one's clothes" may merely imply that the freshness of a clean or new thing is lost, but "to  【dirty】  one's clothes" usually implies some activity which has plainly left its unclean traces upon the garments. In its extended use, too,  【dirty】 tends to stress the unpleasant effect and typically suggests a making squalid or nasty of something that in itself is normal, wholesome, or clean.

【Sully】 implies the staining or soiling of something that is pure, fresh, limpid, or innocent.

It is used more often in reference to immaterial or spiritual than to physical soiling.

【Tarnish】 basically implies the dulling or dimming of the luster of a thing by chemical action (as of air, dust, or dirt).

In extended use it suggests a dimming rather than a total sullying of something of value.

【Foul】  and the intensive form  【befoul】 stress a making filthy or nasty and apply either to a material or an immaterial thing. They often suggest pollution or defiling by something highly offensive or disagreeable.

【Smirch】  and the intensive form  【besmirch】  may emphasize a discoloring by or as if by soot, smoke, or mud; usually they come close to  【sully】 in implying a destruction of immaculateness, but they seldom carry as clear an implication of an effect on real virtue or purity as they do of a darkening or blackening of appearance, reputation, honor, or good name.

【Grime】  and the more usual  【begrime】  intensify the meaning of  【dirty】 and typically suggest deeply imbedded dirt often accumulated over a prolonged period.