subservient

excessively submissive or serving under another

Roots

serv / serve: serve, service, or be in service
sub-: under, below, or after

Other words with the serv / serve root

serve: to help or work for someone or something
service: help or work done for someone
servile: excessively submissive or like a servant

Sub gives under and serv gives serve. Subservient is service from below, with too little backbone left.

The aide was helpful, but never subservient; she still disagreed when the plan was flawed.

Subservient is not ordinary helpfulness. The image is someone placed underneath another person's will. Service becomes submission when the person stops standing upright inside it.