The term 'lacking stability' can be described by two crossword solutions: TIPPY (5 letters) and TOPHEAVY (8 letters). TIPPY is an adjective that describes something that is unsteady or unbalanced, while TOPHEAVY is an adjective that describes something that is disproportionately weighted at the top. Both terms are used to describe objects or situations that are not stable and are likely to topple over.