Given a very short sentence, such as:
Foxglove is harmless enough.
the word harmless is bound to be "ambiguous" in such a short snippet, although that ambiguity might be cleared up after you examine enough surrounding text.
When X is a person, the statement X is harmless enough, usually means "unlikely to cause much annoyance or damage," but there are several contexts in which harmless can be applied. For example, a harmless person:
- is unlikely to incite violence
- is unlikely to betray friends
- is unlikely to hurt their employer's reputation
- is unlikely to assault or harass someone
- is unlikely to be a bad influence
- doesn't mean to hurt someone's feelings when joking around
That said, context can provide a more specialized view. Let's say my 17-year-old daughter is spending a lot of time around a 23-year-old guy named Joe. They are good friends, but I'm concerned that an unhealthy romantic relationship might be starting. My wife might assure me by saying,
"Oh, Joe is harmless enough."
In that context, she probably means that she doesn't think our daughter wants the relationship to turn romantic, and that it's unlikely Joe is going to try to seduce her.
A dictionary can't possibly cover all the different ways a word like this could be used or applied.