slither (v.)

Old English slidan (intransitive, past tense slad, past participle sliden) "to glide, slip, fall, fall down;" figuratively "fail, lapse morally, err; be transitory or unstable," from Proto-Germanic *slidan "to slip, slide" (source also of Old High German slito, German Schlitten "sleigh, sled"), from PIE root *sleidh- "to slide, slip" (source also of Lithuanian slysti "to glide, slide," Old Church Slavonic sledu "track," Greek olisthos "slipperiness," olisthanein "to slip," Middle Irish sloet "slide").

Meaning "slip, lose one's footing" is from early 13c. Transitive sense from 1530s. Phrase let (something) slide "let it take its own course, take no consideration of" is in Chaucer (late 14c.) and Shakespeare. Sliding scale in reference to payments, etc., is from 1842.

Old English gadrian, gædrian "unite, agree, assemble; gather, collect, store up" (transitive and intransitive), used of flowers, thoughts, persons; from Proto-Germanic *gaduron "come or bring together, unite" (source also of Old English gæd "fellowship, companionship," gædeling "companion;" Middle Low German gadderen; Old Frisian gaderia; Dutch gaderen "to gather," gade "spouse;" German Gatte "husband;" Gothic gadiliggs), perhaps from PIE *ghedh- "to unite, join" (see good (adj.)). Change of spelling from -d- to -th- is 1500s, reflecting earlier change in pronunciation (as in  father). Related: Gathered; gathering.