Like all specialized fields, social welfare has its own language or jargon that is used in the field. As a result, a term used in a social welfare context may have a slightly different connotation than what you might find in a typical collegiate dictionary.
A topical thesaurus can help you find the right terms for searching library databases. This will help you save time by honing in on subject headings, sometimes known as "descriptors" which are used in library databases to classify all articles with the same topic.. For example if you were searching PsycInfo, you wouldn't have to search "bipolar disorder," "bipolar affective disorder," "manic depression," and "manic depressive psychosis," you could just search "bipolar disorder" as a subject heading and you will retrieve the most relevant articles regardless of which term they actually use in the article. Give it a try!
There are also several psychology dictionaries which may prove helpful. Two of these are the APA Dictionary of Psychology (Dewey Reference BF 31 A63 2007) and The Dictionary of Psychology (Dewey Reference BF 31 C72 1999).