Abarim Publications' online Biblical Hebrew Dictionary
The noun עכבר (akbar) means mouse. Mice in the Bible aren't very positive; they are considered unclean (Leviticus 11:29) and were known for carrying disease (1 Samuel 6:5 - in relation to the wrath of God aroused by the Philistines improper handling of the Ark of the Covenant; HAW Theological Wordbook of the Old Testament proposes bubonic plague).
Where the word akbar comes from isn't known, but perhaps the slightly similar and also of unknown origin noun עכביש (akkabish), meaning spider suggests there once was a common root or idea for the two of them.
The noun עכביש (akkabish) means spider. Spiders are referred to only three times in the Bible: Job 8:14, 27:18 and Isaiah 59:5.