1. sheet anchor - Noun
2. sheet anchor - Verb
A large anchor stowed on shores outside the waist of a vessel; -- called also waist anchor. See the Note under Anchor.
Anything regarded as a sure support or dependence in danger; the best hope or refuge.
Source: Webster's dictionaryI recognize the Republican party as the sheet anchor of the colored man's political hopes and the ark of his safety. Frederick Douglass