All 5 Uses

speculate
in
The Awakening, by Kate Chopin
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"Granted; as many as you like," he returned, glancing down into her eyes that were full of thoughtfulness and some speculation.
Chpt 8 *

speculation = guessing or theorizing
She lay in bed awake, with bright eyes full of speculation.
Chpt 35

speculation = thought
"I wonder if Leonce will be uneasy!" she speculated, as she seated herself at table.†
Chpt 13
She left them in heated argument, speculating about the conclusion of the tale which their mother promised to finish the following night.†
Chpt 15
A letter also came from her husband, saying he hoped to be back early in March, and then they would get ready for that journey abroad which he had promised her so long, which he felt now fully able to afford; he felt able to travel as people should, without any thought of small economies—thanks to his recent speculations in Wall Street.†
Chpt 35

Definitions:

(1) (speculate as in: don't know, but I'll speculate)
to think about, wonder, guess or theorize with much uncertainty
(2) (speculate as in: speculate in the stock market)
to take a risk for profit--typically a risky investment
(3) (meaning too rare to warrant focus)
Much more rarely, speculation can refer to a gambling card game that was popular in the past.