senpi -sen- gismu

x₁ doubts/is dubious/doubtful/skeptical/questions that x₂ (du'u) is true.

Also: x₂ is doubtful/dubious/questionable (= selsenpi for reordered places). See also jinvi, krici, djuno, birti.

In notes:

birti: x₁ is certain/sure/positive/convinced that x₂ is true.
djuno: x₁ knows fact(s) x₂ (du'u) about subject x₃ by epistemology x₄.
jinvi: x₁ thinks/opines x₂ [opinion] (du'u) is true about subject/issue x₃ on grounds x₄.
krici: x₁ believes [regardless of evidence/proof] belief/creed x₂ (du'u) is true/assumed about subject x₃.
ceirsenpi: s1 has doubts about the existence of a deity/deities.
cnisenpi: x₁ emotionally disbelieves x₂ (du'u) about subject x₃
senki'u: x₁=k₁ justifies x₂=s₁'s doubt/skepticism toward x₃=s₂ (du'u).
flese: x₁ is (a) philosophy/ideology (one sense) about/of/pertaining to topic/subfield (one sense) x₂ with subfield (different sense)/features/details/specifics/specific idea(s) x₃, with methodology x₄, followed/thought/considered by x₅ (thinker/philosopher/individual); philosophy x₁ is characterized by values/thoughts/opinions/ruminations x₃ about topic/subject x₂.