can-not help but

Old English helpan (class III strong verb; past tense healp, past participle holpen) “help, support, succor; benefit, do good to; cure, amend,” from Proto-Germanic *helpan (cf. Old Norse hjalpa, Old Frisian helpa, Middle Dutch and Dutch helpen, Old High German helfan, German helfen), from PIE root *kelb- “to help” (cf. Lithuanian selpiu “to support, help”).

Recorded as a cry of distress from late 14c. Sense of “serve someone with food at table” (1680s) is translated from French servir “to help, stead, avail,” and led to helping “portion of food.” Related: Helped (c.1300). The Middle English past participle holpen survives in biblical and U.S. dialectal use.

In addition to the idioms beginning with help

• helping hand
• help oneself
• help out

also see:

• can’t help but
• every little bit helps
• not if one can help it
• so help me