GG5: 〔本性〕 one's nature.
- 素に戻る regain one's nature.
- 素のままでいる be oneself.
Eijiro: 素のままの自分でいる；《be 〜》: one's natural self
Tanaka: そ、そうじゃなくて、・・・　素の自分、本当の私を必要としてくれる人がいるなんて、考えたこともありませんでしたから。 N-no it's not that ... it's that there could be someone who would need me for what I am, for my true self, I hadn't even thought of that possibility. 
- どうやら、さっきのは演技ではなく、素だったらしい。 It seems like that she wasn't acting back then; they were her real feelings.

See proposed entry 2844548 (素が出る). I was puzzled that the 素 seemed unrelated to the glosses in this entry. Now I think the first gloss is a bit off the mark. Perhaps two senses (n & adj-no) work best.

@@ -14,0 +15,6 @@
+<pos>&n;</pos>
+<gloss>one's nature</gloss>
+<gloss>one's feelings</gloss>
+<gloss>oneself</gloss>
+</sense>
+<sense>
@@ -16 +21,0 @@
-<pos>&n;</pos>

@@ -26 +26,2 @@
-<gloss>(before a noun) mere</gloss>
+<s_inf>before a noun</s_inf>
+<gloss>mere</gloss>
@@ -31 +32,2 @@
-<gloss>(before an adjective) exceedingly</gloss>
+<s_inf>before an adjective</s_inf>
+<gloss>exceedingly</gloss>

I agree.

@@ -6,0 +6,2 @@
+<ke_pri>news1</ke_pri>
+<ke_pri>nf10</ke_pri>
@@ -9,0 +11,2 @@
+<re_pri>news1</re_pri>
+<re_pri>nf10</re_pri>

I'm not positive, but I think that the [news1] tag on 1621290 (素【そ】) is supposed to be on this.