Upright meaning
Ice. Things are frozen for now. This is a time to wait, gather yourself and see clearly, not to push.
Reversed (merkstave)
Isa looks the same either way up, so it has no reversed meaning. Read it upright every time.
A question to sit with
What becomes clear when you stop moving?
Its ætt
Isa belongs to Heimdall's ætt, the runes of forces outside your control and the growth they force.