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_{This is a second puzzle from the Monoalphabetic Equation series, you can check out the previous one here.}

A set of letters has been replaced by $a$, $b$, $c$, and $d$ and one symbol has been replaced by $x$.

Following are some of the English words that consist of those letters, and their meaning:

$abcd = large ○ normalsize + ▿ + $

$cbad = large ● normalsize + small ○ $

$cbda = text{△} normalsize + — + – $

$cab normalsize + x = x +$

- What are the letters that $a$, $b$, $c$, and $d$ replace, respectively?
- What is the symbol that $x$ replace?

Here's a picture, in case the unicode is not working.

Answer:

$a$ = r, $b$ = i, $c$ = t, $d$ = e, $x$ = $∠$

Note: The shapes on the right are combined to make a symbol representing the word on the left.

$abcd = large ○ normalsize + ▿ + $

Word = rite

Depiction = Masonic ritual symbol (per @Timoris) or Wicca ritual pentacle, triangle + arrowhead make a star (intended answer per @Chrone)

$cbad = large ● normalsize + small ○ $

Word = tire

Depiction = tire image

$cbda = text{△} normalsize + — + – $

Word = tier

Depiction = (per @Timoris) tier image

$cab normalsize + x = x +$

Okay, I found this one to be particularly clever:
$x$ is $∠$

thus $cab$ + $x$ = $x$ + becomes
tri $∠$ = $∠$ +

or rather:
triangle = $△$