Why is the ninth month called September?
Old English risan "to rise, rise from sleep, get out of bed; stand up, rise to one's feet; get up from table; rise together; be fit, be proper" (usually arisan; class I strong verb; past tense ras, past participle risen), from Proto-Germanic *us-risanan "to go up" (cf. Old Norse risa, Old Saxon risan, Gothic urreisan "to rise," Old High German risan "to rise, flow," German reisen "to travel," originally "to rise for a journey").
From c.1200 as "move from a lower to a higher position, move upward; increase in number or amount; rise in fortune, prosper; become prominent;" also "rise from the dead." Meaning "come into existence, originate; result (from)" is mid-13c. From early 14c. as "rebel, revolt;" also "occur, happen, come to pass; take place." Related to raise (v.). Related: Rose; risen.
"upward movement," 1570s, from rise (v.). Meaning "a piece of rising ground" is from 1630s. Meaning "spring, source, origin, beginning" is from 1620s. Phrase to get a rise out of (someone) (1829) is a metaphor from angling (1650s).