wash, inquire into, probe
洗 centers on cleansing with water: washing something clean. The extended senses of inquiring into or probing something come from the idea of washing away dirt to reveal the truth underneath.
洗 combines 氵 (water) with 先, which likely contributes the sound and the idea of going forward or ahead, suggesting water moving over something to clean it.
Water 氵 flows ahead 先, washing everything clean. Picture a stream of water moving forward and scrubbing away dirt.
For セン, imagine sending water ahead to wash: send -> セン, and the water cleans as it goes.
to wash; to cleanse; to rinse
washing; laundry
brainwashing
washing; cleansing; cleaning; laundering
refinement; polish
detergent; cleanser; cleaning agent; washing material
baptism; christening
washing one's face
washing one's hands; water (or basin, etc.) for washing one's hands
things to be washed; (dirty) dishes; laundry; washing
washing-up; dish-washing
washing with water; rinsing; flushing
washing one's hair; having a shampoo
toilet; restroom; lavatory; bathroom
synthetic detergent
to finish washing; to wash well; to investigate thoroughly
detergent; cleanser; cleaning agent; washing material
washing machine; (clothes) washer
laundry; the washing
wash basin; wash bowl (incl. portable bowl in a public bath)
washroom; bathroom
pre-washed rice; wash-free rice; musenmai